HI96822 Digital Seawater Refractometer Salinity & Specific Gravity Hanna electrode maintenance kit you can get a digital ORP Meter you can get a digital readout within seconds accurate to ±2 ppt with automatic temperature compensation (ATC) TDS PPM is often converted to uS cm The HI96822 Digital Refractometer eliminates the uncertainty associated with mechanical refractometers by measuring the refractive index to determine the salinity of natural and artificial seawater including brackish Specific Gravity (20 20) is based upon the published relationship between density at 20 °C and the mass of dissolved salts in the seawater sample (CRC Handbook of Chemistry and Physics